Positive displacement pumps are often employed at oilfields for large high pressure applications involved in hydrocarbon recovery efforts. A positive displacement pump may include a plunger driven by a crankshaft toward and away from a chamber in order to dramatically effect a high or low pressure on the chamber. This makes it a good choice for high pressure applications. Indeed, where fluid pressure exceeding a few thousand pounds per square inch (PSI) is to be generated, a positive displacement pump is generally employed.
Positive displacement pumps may be configured of fairly large sizes and employed in a variety of large scale oilfield operations such as cementing, coil tubing, water jet cutting, or hydraulic fracturing of underground rock. Hydraulic fracturing of underground rock, for example, often takes place at pressures of 10,000 to 15,000 PSI or more to direct an abrasive containing fluid through a well to release oil and gas from rock pores for extraction. Such pressures and large scale applications are readily satisfied by positive displacement pumps.
As is often the case with large systems and industrial equipment, regular monitoring and maintenance of positive displacement pumps may be sought to help ensure uptime and increase efficiency. In the case of hydraulic fracturing applications, a pump may be employed at a well and operating for an extended period of time, say six to twelve hours per day for more than a week. Over this time, the pump may be susceptible to wearing components such as the development of internal valve leaks. This is particularly of concern at conformable valve inserts used at the interface of the valve and valve seat. Therefore, during downtime in the operation, the pump may be manually inspected externally or taken apart to examine the internal condition of the valves and inserts. In many cases the external manual inspection fails to reveal defects. Alternatively, once the time is taken to remove valves for inspection, they are often replaced wholesale regardless of operating condition, whether out of habit or for a lack of certainty. Thus, there is the risk that the pump will either fail while in use for undiagnosed leaky valves or that effectively operable valves and inserts will be needlessly discarded.
The significance of risks such as those described above may increase depending on the circumstances. In the case of hydraulic fracturing applications, such as those noted above, conditions may be present that can both increase the likelihood of pump failure and increase the overall negative impact of such a failure. For example, the conformable nature of the valve insert is that it tends to bulge and wear at the edges over time due to repeated striking of the valve seat. Additionally, the use of an abrasive containing fluid in hydraulic fracturing not only breaks up underground rock, as described above, it also tends to degrade the conformable valve inserts over time as abrasive particles are sandwiched between the inserts and the valve seat as the valve repeatedly strikes the seat. Such degradation and eventual leakage may result in failure to seal the chamber of the pump, perhaps within about one to six weeks of use depending on the particular parameters of the application. Once the chamber fails to seal during operation, the pump will generally fail in relatively short order.
Furthermore, the ramifications of such an individual pump failure may ultimately be quite extensive. That is, hydraulic fracturing applications generally employ several positive displacement pumps at any given well. Malfunctioning of even a single one of these pumps places added strain on the remaining pumps, perhaps even leading to failure of additional pumps. Unfortunately, this type of cascading pump failure, from pump to pump to pump, is not an uncommon event where hydraulic fracturing applications are concerned.
Given the ramifications of positive displacement pump failure and the demand for employing techniques that avoid pump disassembly as described above, efforts have been made to evaluate the condition of a positive displacement pump during operation without taking it apart for inspection. For example, a positive displacement pump may be evaluated during operation by employing an acoustic sensor coupled to the pump. The acoustic sensor may be used to detect high-frequency vibrations that are the result of a leak or incomplete seal within the chamber of the positive displacement pump, such a leak being the precursor to pump failure as noted above.
Unfortunately, reliance on the detection of acoustic data in order to address developing leaks at the valve-seat interface as described above fails to avoid the development of leaks in an operating pump. That is, acoustic data may do no more than provide an early indicator of potential leaks. While this may afford an operator time to take the pump off-line in order to address the potential leak, there remains no effective manner in which to avoid the leak in the first place without the need of taking the pump off-line. Thus, at a minimum, even where a catastrophic leak is avoided due to early acoustic detection, down time for the pump at issue still results. There remains no substantially effective manner in which to avoid leaks at the valve-seat interface in an operating positive displacement pump for which abrasives are pumped and a conformable valve insert is employed.